Battery charging systems are provided to charge a battery for a user device. In some cases, the user device may allow either operation of the user device or charging of the battery, but not both to be performed at the same time. In other battery charging systems, both operation of the user device and battery charging may be performed in parallel, but significant system current, power and/or heat generated by the user device during operation and battery charging may require the user device to decrease the battery charging rate.